Development of the Skeleton Flashcards
Skull - Parts? Role?
Neurocranium - forms protective case
Viscerocranium - skeleton of the face
Membranous neurocranium - Roles? Development? Bone names? Key characteristics? Fontanelles?
Membranous neurocranium:
- roof and sides of the skull develops from the neural crest cells
- undergo membranous ossification from flat bones
- surrounds the brain and sensory organs (calvaria)
- formed by the parietal, frontal, temporal and occipital bone
- calvaria has no cartilage
- direct ossification of mesenchyme
- fibrous sutures
- allow distortion to pass birth canal
- allow brain growth
- fontanelles: 6, posterior at 3m and anterior at 18
Cartilagenous neurocranium - 2 Parts? Roles? Development? Bone names? Key characteristics? Fontanelles?
Prechondral chondrocranium:
- in front of pituitary gland, derived from neural crest
Chordal chondrocranium:
- posterior to pituitary and arise from paraxial mesoderm
Fuse and ossify by endochondral ossification to form skull base
Cranial base:
- occipital bone, sphenoid, ethmoid, petrous, mastoid part of temporal bones
Viscerocranium - overview? development? pharyngeal arches?
Overview:
- consists of bones of the face
- formed mainly from first 2 pharyngeal arches
- 5 pharyngeal arches (1,2,3,4,6); developing in craniocaudal sequence, 1st pair 22d, 2nd/3rd pair 24d and 2th/6th pair 29d
Cephalogenesis - early chordates?
Early chordates:
- notochord for support
- simple NS
- segmented muscle blocks
- branchial clefts
Cephalogenesis - first vertebrates? skull formation?
Skull formation: Jaw less
- occipital and parachordal cartilages appeared to support notochord in head
- cartilagenous capsules protect sense organs
- branchial arches supported by cartilagenous rods
- cartilage 0 migrates to the head, so 2nd arch cartilage become 1st
Cephalogenesis - first vertebrates (with jaw)?
Skull formation: jaw
- modification of first arch cartilage
- palatopterygoquadrate bar became upper jaw
- Meckel’s cartilage became the lower jaw
- fibrous connection between them was the TMJ
Cephalogenesis - vertebral evolution?
Vertebral evolution:
- brought massive expansion in head
- protecting the brain with additional bont skeletal elements were developed
- from the neuroectoderm, from which neural crest cells migrate and differentiate into ectomesenchyme
Skull development - signalling molecules/genes?
Development:
- Hox gene play key role in craniofacial development
- pharyngeal arches rely on Hox gene expression
- Calvarial growth an cranial suture morphogenesis is regulated by MSX1/2, shh, BMPs, TGF and FGFRs
Newborn skull’s fontanelles - location? fuse dates?
Anterior fontanelle: - between frontal and parietal bones - fuses by age of 2 Posterior fontanelle: - between parietal and occipital bones - fuses by 2-3 months
Newborn skull - comparison to adult skull?
Facial skeleton 1/8 compared to 1/3 adult skull
Newborn skull - development?
Development:
- frontal bone (in 2 halves), suture obliterated in 8th year, can persist as metopic suture
- mastoid and styloid processes absent, facial nerve close to surface at birth (forcep injury)
- palpation of ant. and post. fontanelles, progress of growth of frontal and parietal bones, degree of hydration and level of intracranial Pa
Post-natal period - neonatal period? growth period?
Neonatal period:
- most major bones ossified, but can move relative to another
Growth period:
- sutures permit growth at edges of flat bones
Spheno-occipital synchondrosis - overview?
Overview:
- allows anterior/posterior growth of skull
- closes at 20
Development of the Head - embryonic period? foetal period? post-natal period?
Embryonic period: - pharyngeal arches - facial development - ossification centres Foetal period: - continued ossification Post-natal period: - closure of fontanelles - facial and skull vault growth - sinus expansion - suture fusion - teeth eruption
Cranial sutures - names?
Metopic/Frontal suture Sagittal suture Coronal suture Lambdoid suture Squamosal suture
Facial sutures - names?
Intermaxillary Nasomaxillary Internasal Nasofrontal Zygomaxillary Zygotemporal Frontozygomatic Frontomaxillary
Cranial vault growth - overview? problems? development? completion?
Overview:
- vault growth directly related to brain development
Problems:
- brain development affect growth of skull and vice versa
Development:
- rapid growth between birth to seven (vault size rapid during first year)
Completion:
- about age 2
Craniosynostosis - definition? non-syndromal craniosynostosis? syndromal craniosynostosis?
a disorder that involves Definition: - premature fusion of the cranial vault sutures causing abnormal and disproportionate growth of the cranial bones during development Non-syndromal: - Scaphocephaly (sagittal) - Plagio (unicoronal) - Trigono (metopic) - Brachy (bicoronal) Syndromal: autosomal dominant - Crouzon - Apert - Carpenter - Pfeiffer Symptoms: - increased intracranial Pa and developmental delay - multiple operations needed
Role of sutures?
- Allow for growth of the cranium
Neurocranium definition?
- Series of 8 bones, which are flat, curved and united by fibrous interlocking sutures
Viscerocranium definition?
- 14 irregular bones
- Maxilla and mandible
General bones of the skull?
- Frontal
- Parietal
- Sphenoid
- Nasal
- Lacrimal
- Occipital
- Zygomatic
- Maxilla
- Mandible
Bird’s eye view of the cranium - annotated diagram?
- Frontal bone
- Coronal suture (bregma)
- Sagittal suture (bregma and Lambda)
- Parietal bone
- Parietal foramen
- Lambdoid suture (lambda)
- Occipital bone
Skull features - view below?
- Incisive fossa (nasopalatine LA)
- Palatine process of maxilla
- Palatine bone
- Sphenoid
- Foramen (lacerum, ovale, spinosum)
- Carotid canal
- Stylomastoid foramen
Skull differences between adult and child?
- Anterior fontanelle
- Posterior fontanelle
- Sphenoid fontanelle
- Mastoid fontanelle
Skull characteristics - At birth?
Facial skeleton: - 1/8 of skull Frontal bone: - 2 halves (suture - metopic after 8th year) Mastoid and styloid processes are absent
Sinuses - Where are they located?
Frontal bone: - sinuses above the eye socket - irregular shaped Maxillary: - either side of the nose
Facial skeleton - variability? constituents?
Variability: - thickness Constituents (thick cortical): - cranium, nasal bone, zygomatic bone, orbital rim and zygomatic buttress Maxilla sinus is thin
Midfacial skeleton - characteristic?
Characteristics:
- increased SA to bone-vol ratio, with closer prox to BV providing superior supply of nutrients and promotes increased healing rate
Zygoma - role? fracture?
Role:
- protection of globe of the eye, origin to masseter muscle and transmit masticatory forces
Blow-out fracture:
- involving infraorbital nerve, inferior rectus and inferior oblique muscle
Rene Le Fort classification - types?
I:
- only the maxilla
- from the maxilla to the nasal bone
- across the facial skeleton
Nasal bones - characteristics? shape? role?
Characteristics: - thick (bridge area) Shape: - triangular with septum Role: provides strength, considerable resistance to direct blow - cribriform bone may fracture
Mandible - annotations (outer and inner) and fractures?
Annotations: Outer - body - ramus - condylar process - oblique line - mental foramen - inferior and superior border - superior surface Annotations: Inner - head/neck of condylar - angle - pterygoid fovea - mandibular notch - coronoid process - mandibular foramen - mylohyoid groove - retromolar triangle - attachment for pterygomandibular raphe Fractures: - body - symphysis - angle - ramus - subcondylar and condylar - coronoid process
Mandible and fracture relation? Fracture location?
Mainly in the maxillofacial area:
- fracture force
- morphology
- strength and resilience of mandible and attached muscles
Symphysis:
- thickest and strongest
Incisor region:
- oblique due to actions of genial and mylohyoid muscles (fragments with incisor teeth overlap)
Canine region:
- weak due to length
Angle region:
- indirect force
- weak due to right angle and wisdom teeth
- fragments displaced due to opposing effects of pterygomasseteric sling and suprahyoid musc
Inferior dental bundle:
- fibrous sheath protect vessels and nerves
Multifact blood supply:
- endo/periosteum and musc
Condylar:
- contusion, dislocation or intra/extracapsular fractures (displaced medially due to resistance of strong lateral ligaments, deviates to injured side on opening)
Edentulous mandible - blood supply? changes?
Blood supply:
- only periosteal supply
- if stripped for plating result in non-union fractures
Changes:
- reduct in alveolar ridges
- due to resorption after tooth loss
- rapidly in first year (mandible > maxilla)
- lack bulk of bone and structures such as inferior alveolar nerve and mental foramen (implants)
- reduced retromolar area (implant)
- sclerotic bone (poor screw anchorage)
